The quality requirement of the liquid crystal display (LCD) panel is higher and higher with the growing popularity of the liquid crystal display panel. For example, with the increasing of the viewing angle of a thin film transistor LCD (TFT-LCD), the contrast and resolution of the screen thereof are gradually decreased. It is due to a result that a birefringence of the liquid crystal molecule in the liquid crystal layer is changed with the variation of the viewing angle. The dark-state light leakage can be effectively reduced by a wide viewing angle compensation film. A contrast of the screen can be considerably increased within a specific viewing angle.
The compensation principle of the compensation film is generally to correct the phase difference due to different viewing angles of the liquid crystal, so that the birefringence property of the liquid crystal molecule can be symmetrically compensated.
Different compensation films are used for different liquid crystal display modes, wherein the compensation film of a large-size LCD TV is used for a vertical alignment (VA) display mode, such as the N-TAC of Konica company used in early stage, the improved Zeonor of OPOTES company, the F-TAC of Fujitsu company, and the X-Plate of Nitto Denko company.
If the compensation values of the compensation films are different for the same optical path difference of the liquid crystal, the dark-state light leakage and the contrast of the large viewing angle are different. Referring to FIG. 1 and FIG. 2, FIG. 1 is an isoluminance contour diagram of a traditional technology by using an uniaxial positive birefringence A-compensation film (A-Plate) and an uniaxial negative birefringence C-compensation film (C-Plate) to compensate the dark-state light leakage, and FIG. 2 is an equal contrast ratio contour diagram in full viewing angle of the traditional technology after being compensated by using the A-Plate and the C-Plate, wherein the compensation values of A-Plate and C-Plate are listed as follows:
optical pathpre-tilt angledifference ofof liquidliquid crystalcrystalA-Plate RoA-Plate RthC-Plate Rth352.1 nm89°109 nm55 nm403 nm
As shown in FIG. 1 and FIG. 2, when the compensation values of A-Plate and C-Plate are used, a serious light leakage may be generated if watching at a large viewing angle in a dark state, wherein the contrast of the large viewing angle becomes poor and the range of the viewing angle is actually small.
It is therefore tried to solve the problem, as described above.